Dies for high-temperature applications and alloy therefor



Patented Dec. 16, 1952 DIES FOR HIGH-TEMPERATURE APPLICA- TIONS AND ALLOY THEREFOR Stephen G. Demirjian, Everett, and William H.

McCarty, Swampscott, Mass., assignors to General Electric Company, a corporation of New York No Drawing. Application October 6, 1950, Serial No. 188,882

The present invention relates to dies for high temperature applications and to an alloy therefor. More particularly the invention relates to dies intended for operation upon metals heated to a high temperature, examples of such dies being hot hammer forging dies, swaging dies, upsetting dies, hubbing dies and trimming dies employed in the forging or shaping of various high temperature alloys and stainless steels.

For many years die steels have been fairly standardized and there have been available on the market a reasonable variety of die steel alloys for use in the hot working of metals. However, with the inception of precision forging of high temperature alloys and stainless steels in the manufacture, for example, of gas turbine blades, the low performance life of dies composed of the known alloys has been one of the biggest obstacles to increased production.

Extensive tests on the commercially available die steels have shown a marked variation in die life between the various die steels when employed for the forging of high temperature alloys and stainless steels. As a result of these tests, it was found that of the known commercially available alloys, the best for use in the forging of high temperature alloys was on having a typical analysis of 0.35% carbon, chromium, 1.2% tungsten, 0.2% vanadium, 0.35% manganese, 1% silicon and 1.6% molybdenum, but even with this alloy the average performance life of a production die made therefrom was about 530 pieces per die.

The present invention is based on the discovery that the performance life of dies employed in the hot working of high temperature alloys and stainless steels can be materially increased if the dies are made from an alloy containing, by weight, from 0.3% to 0.40% carbon, 1.5% to 2.5% manganese, 1.25% to 2.5% silicon, 3% to 4% chromium, 0.75% to 1.5% tungsten, 1% to 2.0% nickel, balance iron. Preferably the manganese content is between 1.7% and 2.2% and the silicon content between 1.5% and 2%, with a preferred die material being one in which the carbon is within the prescribed limits and the manganese content is about 1.9%, the silicon content about 1.7%, the chromium content 3.5%, the tungsten content 1% and the nickel content 1.5%. It has been found that dies composed of this material when employed in the forging of high temperature alloys will have an average die life of at least 610 pieces per die. This represents at least a 15% increase in the die life over the best of the known die al y 6 Claims. (Cl. 75128) .2 and a corresponding decrease in the cost of producing the forged articles.

The alloys of the present invention are particularly characterized by high impact strength, wear resistance, and hot hardness as well as excellent resistance to thermal checking. The alloys are 'air hardening and no annealing temperature or process has been found which would lower the hardness value below Rockwell C 28.

In the practice of the present invention, a melt of the designated materials can be cast into an ingot from a temperature of approximately 2850 deg. F. and die stock formed from the resultant ingot by raising the temperature of the ingot to about 1975 deg. F., forging the ingot at this temperature and thereafter spheroidize annealing the forged product at about 1100 deg. F. by holding for 15 hours at temperature. The die impression can either be cut into the resultant die block or the die impression can be formed by a hot hubbing operation.

After annealing the alloy has a Rockwell C hardness of 28 and this hardness can be increased to from 58 to 60 by heating at temperatures of from 1600 deg. F. to 2000 deg. F. followed by air cooling. Alternatively, the forged material can be heated to 1450 deg. F. and furnace cooled to obtain a hardness value of Rockwell C 58.

The alloys can be readily heat treated with a minimum amount of distortion and the heat treated products combine maximum toughness with excellent resistance to shock, impact, and thermal checking. As has been previously indicated, the materials are air hardening to the extent that they cannot be annealed by normal slow cooling. The wear resistance is superior to any known commercially available hot work die steel resulting in increased die life.

In order to obtain these properties, it has been found that the proportions of the various elements must be kept within the prescribed limits. A minimum of at least 1.5% manganese and preferably 1.9% manganese and 1.25% silicon, preferably 1.7% silicon, have been found essential to provide an air hardenable material, while the manganese, silicon, chromium, tungsten, nickel and carbon combined contents have been found critical in order to obtain the desired impact strength, hardenability, wear characteristics, and resistance to thermal checking.

While the alloy of the present invention is particularly useful in the manufacture of forging dies, it obviously may also be employed for other types of tools and dies used in the workmg of high temperature alloys and stainless steels.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An .air hardening alloy suitable for use as a forging die comprising by Weight from about 0.3 to 0.4% carbon, 1.5 to 2.5% manganese, 1.25 to 2.5% silicon, 3 to 4% chromium, .75 to 1.5% tungsten, 1 to 2% nickel, balance iron, said alloy being characterized by high impact strength, Wear resistance and hot hardness as well asexcellent resistance to thermal checking.

2. An air hardening alloy suitable ior use. as a forging die, comprising by weight from 11.33 to 0.38% carbon, 1.7 to 2.2% manganese, 1.5 to 2.0% silicon, 3 to 4% chromium, .75 to 2% tungsten, 1 to 2.0% nickel, balance iron, 'said..;a1loy being characterized by high impact strength, wear resistance and hot hardness as well as excellent resistance to thermal checking.

.3. -An air hardening alloysuitable for use as a forging die comprising by weight from about 0.35% carbon, 1.9% manganese, 1.7% silicon,

3. 5%. chromium, 1% tungsten, 1.5% nickel, balanceiron, said alloy being-characterized by high REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,379,988 Post et a1. July 10, 1945 FOREIGN PATENTS Number Country Date 455,651 Great Britain 1-..--- Apr. 16, 1936 502.196 Great Britain Mar. 1.4, 1939 

1. AN AIR HARDENING ALLOY SUITABLE FOR USE AS A FORGING DIE COMPRISING BY WEIGHT FROM ABOUT 0.3 TO 0.4% CARBON, 1.5 TO 2.5% MANGANESE, 1.25 TO 2.5% SILICON, 3 TO 4% CHROMIUM, .75 TO 1.5% TUNGSTEN, 1 TO 2% NICKEL, BALANCE IRON, SAID ALLOY BEING CHARACTERIZED BY HIGH IMPACT STRENGTH, WEAR RESISTANCE AND HOT HARDNESS AS WELL AS EXCELLENT RESISTANCE TO THERMAL CHECKING. 